Radio frequency variable voltage multiplier



Jan. 21, 1958 F. l. BOLEY RADIO FREQUENCY VARIABLE VOLTAGE MULTIPLIER Filed Dec. 3, 1954 5 ma 3 Wm l5 me Fl LAM ENT HIGH Fl LAMENT OSCILLATOR VOLTAGE OSCILLATOR INVENTOR OSCILLATOR 2O FORREST I. BOLEY ATTORNEY United States Patent C RADIO FREQUENCY VARIABLE VOLTAGE MULTIPLIER Forrest I. Boley, Middletown, Conn., assignor to Research gor lrioration, New York, N. Y., a corporation of New This invention relates to a radio frequency voltage multiplier for producing direct high voltages of the order of several hundred thousand volts at currents of a few milliamperes, and more particularly to such a device capable of producing an output voltage level which can be varied over a wide range.

Cascade voltage multipliers are known in which a number of capacitors are charged from a low voltage source through a series of rectifiers and are discharged unidirectionally in series so that the voltages add, to provide essentially a series of cascade voltage doublers utilized to produce a desired high voltage. Limitations on the high voltage which can be so obtained are the voltage stress across the successive capacitors, which becomes greater as more output voltage is provided, limitation of possible load current which can be supplied due to the limitations on the peak current ratings of the rectifiers, and rapidly mounting cost as the voltage is increased due to the need for providing a separate filament transformer for each rectifier tube, and because each transformer must be insulated for high voltage. It will be apparent that this last limitation is very serious at voltages in the order of several hundred thousand.

It is a primary object of the invention in a high voltage multiplier of the above type, to provide a simple and inexpensive means for filament excitation.

When the initial voltage which is to be multiplied (i. e., the input voltage) is provided at radio-frequencies, e. g., in the megacycle range, the capacitors which are used provide a very low impedance at these frequencies; similarly, due to the interelectrode capacity of the rectifier diodes, these diodes also present a relatively low impedance. These low interelectrode and condenser impedances give rise to large circulating current in the system, which can be used to provide the necessary filament current. However, this current is tied to the output voltage, to which it is necessarily related, and the correct filament current can be provided only at one fixed output voltage, so that it is not possible to vary the output voltage in such a system. Many applications exist for high-voltage multipliers, e. g., in physics research work, etc., which require an output voltage which can be varied and accurately controlled over a fairly wide range. For such applications, the above described use of circulating currents as a filament supply source is unsatisfactory.

It is an object of the present invention to obviate the above difiiculty and to provide high-frequency filament exitation in a radio frequency voltage multiplier, which permits the output to be varied over a wide range, with a correct filament supply throughout the entire range. A further object is to provide transformerless filament supply for a voltage multiplier of variable output.

Another object of the invention is to provide a simple variable high voltage multiplier of inexpensive construction using standard components, the high voltage output of which can be controlled and varied entirely at the low voltage input, without the need for controlling or manipulating high voltage circuitry.

resistors 16 all do not have the same value.

According to the invention, at maximum output, the filaments are heated solely or mainly by the high frequency circulating currents which flow in the circuit at the normal maximum output voltage. For operation at lower voltages, an auxiliary high frequency circulating current is provided from one or more adjustable auxiliary sources coupled to the normal circulating system from which the filaments are supplied at the maximum output voltage.

The specific nature of the invention, as well as other objects and advantages thereof, will clearly appear from a description of a preferred embodiment as shown in the accompanying drawing. The single figure of the draw ing is a schematic circuit diagram showing the principle of the invention.

Referring to the drawing, the high voltage multiplier proper consists of fifty rectifier tubes 2 and condensers 4 and 6 arranged in .the two columns shown. The drawing shows the top and bottom three diode stages of the circuit and the intervening stages are identical with the ones shown. 1B3 vacuum diodes are suitable for use as rectifiers. The multiplying condensers used in a practical embodiment were 500 ,u f. at 20,000 volts.

Power for driving the multiplier column is obtained from a 1000-watt, 3 megacycle radio-frequency oscillator 8, which is coupled to the column by transformer 10. The secondary of transformer 10 is center tapped and the center tap is made the ground potential point of the system. Conventional means, involving variation of the radio-frequency oscillator plate supply voltage, are provided for varying the output of the oscillator 8, to thereby vary the high voltage output.

At the 3 megacycle operating frequency the iuterelectrode capacitances of the diodes present a relatively low impedance (approximately 50,000 ohms per diode or 1000 ohms for the parallel combination of 50 tubes). The capacitance between condenser columns 4 and 6 is approximately equal to the total of that contributed by the diodes. These low interelectrode and intercolumn im pedances give rise to large circulating currents in and between the two condenser columns. The center-tapped inductance 14 has been added to cancel the capacitive reactance and thereby eliminate the capacitive loading effect on the high voltage oscillator. The circulating currents of course still fiow.

The center tap of inductance 14 is the high voltage connection to the circuit. For the present model the inductance 14 consists of 50 turns of number 20 copper wire wound on a coil form 6 inches long and 2% inches in diameter. i

The filament excitation is achieved in the following manner. The fifty resistors 16 are connected in series with the two voltage multiplying condenser columns 4 and 6. Connected in parallel with each of these resistors is a diode filament 18 which is thereby heated by the capacitive circulating currents. As it turns out in practice, the circulating currents are much higher at the extreme upper and lower ends of the condenser columns due to the inductive loadings of 14 and of transformer 10 at the two ends. Therefore the fifty shunt connected Much lower values will be required at the extreme ends than at the center. Although the resistance values to be used in a particular voltage multiplier must be chosen individually to obtain proper filament heating. it may be helpful to state that in a practical model the values range from 0.1 ohm to 22 ohms. The lower resistance values are obtained from short lengths of resistance wires while ordinary carbon resistors sufiice for values in excess of one ohm. No other circuitry is required for fixed output voltage operation and the column is self-starting. That is, application of power from the high voltage oscillator will give rise to circuating currents for heating the fila ments and the output voltagewill increase to full value.

If operation at decreased levels of output voltage is required, auxiliary filament: power is required. This is necessary because lower: output voltage isacquired by a reduction. in power level ofcthehighvoltage. oscillator which in turn reduces the circulating currents and hence the filament excitation. The auxiliary filament power is provided by'the two -rnegacycle, 50-watt oscillators and 22. This power is ccupledto the column via transformers 24 and 26 and is connected to the diodes whose filaments are in series with condensers 4 by way of condenser column 28 and to those whose filaments are in series with condensers 6 by way of condenser column 30; The high voltage insulation required between successive stages is thus provided by the condensers themselves. Inductances 32 and 34 (24 on each side) are added between adjacent condenser columns to balance the intercolumncapacitive reactants; Each inductance consists of 100 turns of No. 30 wire closely wound on a inch diameter form.

With the complete circuit as shown, reduced output operation is achieved by a reduction of high voltage oscillation power level. coupled with a corresponding increase of filament oscillator power level sufiicient to maintain proper filament excitation.

The entire circuit of fifty stages can be mounted on a Plexiglas. frame and the entire assembly of a model as actually constructed is 65 inches high by 9 inches by 9 inches.

It will be apparent that the embodiments shown are only exemplary and that various modifications can be made in construction and arrangement within the scope of my invention as defined in the appended claims.

I claim:

1. In a voltage multiplier for producing high directvoltage from a first radio-frequency alternating current source, a rectifier and multiplier circuit comprising at least two groups of high-tension condensers, a plurality of unidirectional discharge tubes connected between said groups, each of said tubes having an incandescible cathode, means for heating each cathode comprising individual impedance means associated with each tube for producing a voltage drop due to the normal radio-frequency circulating currents in said circuit, and means connecting each respective cathode with its associated impedance element for supplying each cathode with heating current, and at least one additional radio-frequency source, and means for-coupling said additional source to said impedance elements to provide an additional supplementary voltage drop in said elements for supplying supplementary heating current to said cathodes.

2. The. invention: according to claim 1, said additional radio-frequency source being controllable for adjustment of the heating current to the optimum operating value.

35 Th'e'inventi'on according to claim 1, there being two such additional sources,.one for each of said groups of high-tension condensers.

4. In ahighvoltage direct current supply ofthe voltage multiplier type, a first high frequency source of power, a plurality of.filamenttype rectifier tubes and condensers connected to multiply and rectify the voltage of the power source, and individual circuits for heating the filaments of the rectifier tubes comprising. an impedance device associatedlwith each tube for producing a voltage drop due to the normal radio-frequency currents circulating through theinterelectrode capacitances of the rectifier tubes and through"said-capacitors to provide the main filament excitation; a' second high-frequency source of power, means for coupling said second source ofpower to saidimpedance devices to furnish additional power for the filaments, said second source being adjustable to control the degree of filament excitation.

5. A high-voltage direct supply of the voltage multipiier type comprising a radio frequency source of power, a plurality of rectifier tubes of the filament type and a condenser for each tube, connected to said radiofrequency source to multiply and rectify the voltage therefrom,.said rectifier tubes being arranged in substa'ntially parallel relationship with alternate tubes oppositely oriented and a condenser connected between the cathodes and anodes of at least alternate pairs of said tubes to form two groups of tubes, the tubes of each tube being similarly oriented, there being two groups of condensers, one group associated with the respective anode circuit of each group of tubes, a series of voltage devices respectively in series with the condensers of each group,- there being one voltage device for each rectifier tube for pro ducing a voltage drop due to the normal radio-frequency circulating currents in the circuit, and'conduc'tor means connecting the filament of each rectifier tube acrossone' of said voltage means for supplying each cathode with heating current, and an inductance element connected across said two groups of condensers at the outputend, and an output terminal connected to saidinductance ele mentintermediate its ends.

6; The invention according to claim 5, and an inductance element connected across said two groups of condensers at the output end, and an output terminal connected to said inductance element intermediate its ends;

7. The invention according to claim 5, an input transformer connected between said high voltage oscillator and said multiplier, said voltage devices being dropping resistors, the resistance values of said resistors being graded from a low value at the center of each group toward higher values toward the ends of the group to com'pe'n' sate for the inductive loading of said transformer and said inductance.

8. The invention according to claim 7, and at least one additional radio-frequency source of controllable arnpli= tude, and means for coupling said additional source to said resistors to provide an additional supplementary'voltage drop in said resistors for supplying supplementary heating current to said'cathode.

9. The invention according'to claim 8, there being two such additional radio-frequency sources, one for each of said groups of high-tension condensers.

10. The invention according to claim 9, said coupling means comprising a second set of two groups of ca pacitors, one corresponding to each of said first groups, with one capacitor of each of said second set connected with one capacitor of each of said first groups through inductive: connecting means whereby aplurality of rest) nant circuits are formed, one: for each capa'citor'an'd tube of themultiplier circuit, said resonant circuitsbeing sub stantially tuned to the frequency of said second-frequency source.

11. The invention according toclaim 10, the frequencyofsaid second radio-frequency source being dilferent'fromthat of the first radio-frequency source.

12. The invention according to claim 11', said second radio-frequency source being coupled'tothe voltage mul tiplier circuit through transformer means.

References Cited in the file of this patent UNITED STATES. PATENTS 

